How can I get particles (confettis) to fall on a sphere, follow its surface without penetrating it and fall off when reaching the "equator"?
For the rotation, make it Dynamic in the particle settings



For the intersection, create a second sphere and make it a collision object (this will be your hit box) and enable Size Deflect in the particle system, then scale down the second sphere until the particles hit the first sphere near its surface (because the size deflect will make the particles deflect a few centimeters from the surface). Of course delete the collision from the first sphere.

For the stickiness, for confetti you should use 0 stickiness, 0 friction (or at least low values of it) and 1 damping